Endotoxemia increases relative perfusion to dorsal-caudal lung regions

Changes in the spatial distribution of perfusion during acute lung injury a nd their impact on gas exchange are poorly understood. We tested whether en dotoxemia caused topographical differences in perfusion and whether these d ifferences caused meaningful changes in regional ventilation-to-perfusion r atios and gas exchange. Regional ventilation and perfusion were measured in anesthetized, mechanically ventilated pigs in the prone position before an d during endotoxemia with the use of aerosolized and intravenous fluorescen t microspheres. On average, relative perfusion halved in ventral and crania l lung regions, doubled in caudal lung regions, and increased 1.5-fold in d orsal lung regions during endotoxemia. In contrast, there were no topograph ical differences in perfusion before endotoxemia and no topographical diffe rences in ventilation at any time point. Consequently, endotoxemia increase d regional ventilation-to-perfusion ratios in the caudal-to-cranial and dor sal-to-ventral directions, resulting in end-capillary Po, values that were significantly lower in dorsal-caudal than ventral-cranial regions. We concl ude that there are topographical differences in the pulmonary vascular resp onse to endotoxin that may have important consequences for gas exchange in acute lung injury.